Phantom drive?
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From: Andreas Beermann on 10 Nov 2009 07:25 Hi Paul, I just looked into various schematics from different hardware revisions... seems details such as pullup resistors or capacitors vary a lot over the different versions. Maybe you could first try to find out which schematic fits to your hardware revision... I was always looking into this one here: http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/c64/250469-rev.A-left.gif but maybe you have anoter revision? In case yes, it would also be worth to look at R28/29/30 maybe? Would you be able to take some (good!) pictures of your board showing both sides - esp. around the serial interface? Maybe we can spot the problem on hte picture! I often do it this way when since I do not have a microscope or magglass... Andreas
From: Paul Förster on 10 Nov 2009 09:15 Hi Andreas, On 2009-11-10 13:25:46 +0100, Andreas Beermann <andreasbeermann(a)lycos.de> said: > I just looked into various schematics from different hardware > revisions... seems details such as pullup resistors or capacitors vary > a lot over the different versions. Maybe you could first try to find > out which schematic fits to your hardware revision... > I was always looking into this one here: > http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/c64/250469-rev.A-left.gif but > > maybe you have anoter revision? In case yes, it would also be > worth to look at R28/29/30 maybe? .... here's the board's label: PCB ASSY NO. 250469 PCB NO. 252311 REV.3 I took the same images (left and right), put them together in one image and printed it in A3. So we both have the same schematics, I guess. Where are you taking me with R28/29/30? I can't find them neither in the schematics *nor* on the board. The highest resistor number I can find on my test board is R19 next to the power switch. And on the board in question it probably was the same. My test board shows line two from the above as PCB NO. 252311 REV.4. But beside that, it looks exactly the same. > Would you be able to take some (good!) pictures of your board showing > both sides - esp. around the serial interface? Maybe we can spot the > problem on hte picture! I often do it this way when since I do not > have a microscope or magglass... .... I have a normal magnifying glass, magnifying factor 2 times. But what I do not have is a macro optics for my camera and good lighting. So you wouldn't probably see much on pictures. I can try if you want but where can I send them? I don't have a place where I can upload them. -- cul8er Paul paul.foerster(a)gmx.net
From: Paul Förster on 10 Nov 2009 09:49 Hi Andreas, On 2009-11-10 13:25:46 +0100, Andreas Beermann <andreasbeermann(a)lycos.de> said: > but maybe you have anoter revision? In case yes, it would also be > worth to look at R28/29/30 maybe? .... ah, I see what you're getting at. There are no resistors R28, R29 and R30. There's only RP6 with 1k Ohm and RP3 with 3.3k Ohm. Also, my boards do not have the U20 (556) chip. So the other schematics can be ruled out by both the board/revision number as well as the parts shown in the schematics. -- cul8er Paul paul.foerster(a)gmx.net
From: Peter Schepers on 12 Nov 2009 19:02 In article <7ltas8F3f7bp5U1(a)mid.individual.net>, Paul F�rster <paul.foerster(a)gmx.net> wrote: So Paul, any updates to your findings? I'm looking over the schematics again, wondering what else to look for. Everything is going through U2 for the User port and serial port. Try measuring the output at the serial port when attempting to load something, just to see what shifts logic levels or changes. Try measuring U2 pins 23, 2, 3 and 22. These seem to be some of the control logic to enable the CIA, with 23, 2 and 3 being active low. They should be high until you try to do something with the drive. Peter S.
From: Peter Schepers on 12 Nov 2009 22:09
Paul: Forget what I wrote before, don't know what I was thinking. Try measuring your serial port readings without and with a device connected as follows: Pin Upluggd Pluggd/off Pluggd/on --------- ------- ---------- --------- 1 (SRQIN) High Float High 2 (GND) Low Low Low 3 (ATN) High Float High 4 (CLK) Low Low Low 5 (DATA) High High High 6 (RESET) High Float High First column is no device plugged in the serial port on the C64. Second column is drive plugged in, but off. Third is drive plugged in and on. Note that pin 5 switches between high-low-high when a drive is powered up. Float means the voltage is between 0 (GND) and 5 (Vcc). My logic probe shows no reading, neither high nor low. Now, check the 6526 U2 pins below: Pin State 5 (ATN) Low 6 (CLK out) High 7 (Data out) Low 8 (Data In) Low 9 (Clk in) High Once again, pin 9 switches between High-Low-High when a drive is powered on. Check pin 23 on U2 when issuing a load command, it should trigger high/low/high as well. PS. |